ELECTRICAL PRINCIPLES AND TECHNOLOGIES Unit 4 Topic 1

Questions to think about...  How do we turn coal in the ground or water behind a dam into electric energy that you can use in your home?  How are we able to control the energy so that the various appliances we use receive just the right amount?  What new technologies can we develop to help us use energy in less environmentally demanding ways?

Topic 1: Electric Charges

 The electrical devices you use everyday, from light bulbs to computers, use the energy of moving charges to do useful work.

Producing Charges  Materials that attract and repel other materials are said to be charged, or carry an electric charge.  Van de Graaff  How can you tell that the girl touching the generator has also become electrically charged?

Van de Graaff Schematic view of a classical Van de Graaff- generator. 1) hollow metal sphere 2) upper electrode 3) upper roller (metal) 4) side of the belt with positive charges 5) opposite side of the belt with negative charges 6) lower roller (for example an acrylic glass) 7) lower electrode (ground) 8) spherical device with negative charges, used to discharge the main sphere 9) spark produced by the difference of potentialsacrylic glass

 Charges produced by rubbing or touching remain stationary, so they are sometimes called static electricity.  Sometimes charges move, so unbalanced charges is a more accurate description.  The quantity of electric charge is expressed in coulombs (C)

 There are 3 different interactions in terms of positive and negative charges in materials. a. Neutral (uncharged): equal positive and negative charge b. Positive charge: excess positive charge c. Negative charge: excess negative charge

Benjamin Franklin ( )  1 st to use the terms “positive” and “negative” to describe charges  Unlike charges- two different charges  Like charges- charges of the same type (both positive, or both negative)  What are positively charged particles called?  What are negatively charged particles called?

Laws of Charges: 1. Unlike charges attract 2. Like charges repel 3. Charged objects attract uncharged (neutral) objects According to modern theory, unbalanced charges on solid materials are due to the movement of electrons from one object to another.

Insulators vs. Conductors  Insulators:  Materials that do not allow charges to move freely on or through them Examples:  Conductors:  Materials that allow charges to move freely Examples:  Fair conductors:  Not prefect insulators, but are not good conductors either. Examples:

 Semiconductors:  Materials with higher conductivity than insulators but with lower conductivity than metals Ex: silicon and gallium  Superconductors:  Materials that offer little, if any, resistance to the flow charges Usually made of alloys and ceramics Take up less space and can carry higher charges that ordinary conductors

 Electric discharge:  An accumulated charge where electrons either enter an object to make up for a shortage, or an excess of electrons leave an object Small sparks  Why is this a safety hazard? (pg.270)  Grounding:  A way of neutralizing conductive materials  List some ways in which objects are neutralized. (p. 270)

 Ionization devices:  Produce both positive and negative charges REMEMBER: an ion is a charged particle!  Charged objects attract dust and contaminants

To Do:  Topic 1 Questions: